The present disclosure relates to subject matter contained in Japanese Patent Application No. 3-278194 (filed on Oct. 25, 1991) and Japanese Patent Application No. 4-249379 (filed on Sep. 18, 1992), which are expressly incorporated herein by reference in their entireties.
1. Field of the Invention
The present invention relates to a distal end part of a side-viewing endoscope having a planar image sensor, such as a solid-state image pickup device, which is incorporated in the distal end portion of an insert part thereof.
2. Description of the Prior Art
The distal end part of a side-viewing endoscope of the type described above has heretofore been arranged with an objective optical system disposed in the distal end portion of the insert part with its optical axis perpendicularly intersecting the longitudinal axis of the insert part distal end portion. A planar image sensor is disposed along the longitudinal axis of the insert part distal end portion, in opposing relation to the objective optical system. The planar image sensor is incorporated in the distal end portion of the insert part, so that it can be inserted and removed in directions perpendicular to the longitudinal axis of the insert part distal end portion (see Japanese Patent Application Laid-Open (KOKAI) No. 62-59914).
In the case of the distal end part of a side-viewing endoscope having a planar image sensor incorporated in the distal end portion of the insert part thereof, if an illuminating light guide fiber bundle 91 is disposed to lie through the space at the back of the planar image sensor 92, as shown in FIG. 9, the limited space can be utilized efficiently, and the diameter of the distal end portion 90 of the insert part can be minimized. Reference numeral 93 in the figure denotes an objective optical system.
However, if the planar image sensor 92 is incorporated in the distal end portion 90, so that it can be inserted and removed in directions (vertically as viewed in FIG. 9) perpendicular to the longitudinal axis of the distal end portion 90, the space at the back of the planar image sensor 92 must be kept vacant as a dead space, and the illuminating light guide fiber bundle 91 must lie through the other portion.
Consequently, the distal end part of the side-viewing endoscope, according to the prior art, which has the planar image sensor 92 incorporated in the distal end portion 90 of the insert part, increases in the diameter, thus intensifying the pain inflicted on the patient, when it is inserted into his/her body cavity.